p53-activated MSCs exhibit reduced protection of FLT3/ITD AML cells from FI-700–induced apoptosis. (A) MSCs were pretreated with 10μM Nutlin-3a (N3a) for 24 hours. After the wells were washed 3 times with MEM-α medium (control medium: Ctrl-Med), MOLM-13 cells were treated with 800nM FI-700 for 24 hours in the presence or absence of MSCs from 3 normal subjects (N-MSC) or 3 AML patients (AML-MSC). Asterisk (*) indicates significance at P < .05 (1-way ANOVA/Tukey). (B) MSCs were transfected with either control (SiC) or p53 siRNA (Sip53). Twenty-four hours posttransfection, cells were subsequently treated with 10μM Nutlin-3a (N3a). After washing, MOLM-13 cells were treated with 800nM FI-700 for 24 hours. Intensity of the immunoblot signals was quantified and the relative intensity of p53 compared with β-actin was calculated.